The present invention relates to a magnetic disk to be mounted on a magnetic disk device, such as a hard disk drive (HDD) and the like, for recording information, and the manufacturing method thereof.
Conventionally, with a magnetic disk device, at a halt stage, a CSS (Contact Start and Stop) method has been employed wherein a magnetic head is kept in contact with an inner circumferential region surface for contact sliding on the magnetic disk. At a start-up stage, the magnetic head is slightly raised while sliding in contact with this inner circumferential region surface to start recording/reproduction at a region for recording/reproduction outside of the inner circumferential region surface for contact sliding. With this CSS method, the region for contact sliding needs to be secured on the magnetic disk separate from the region for recording/reproduction.
Also, with the CSS method, a protruding/recessed shape having certain amount of surface roughness, which is called texture, has been provided on the magnetic disk principal surface to avoid a state wherein the magnetic disk and the magnetic head are subjected to contact adsorption at the halt stage. Further, with the CSS method, countermeasures have been devised such as coating the magnetic disk surface with a protective layer to protect the magnetic disk from contact sliding of the magnetic head (e.g., Japanese Patent No. 3058066).
On the other hand, recently, an LUL (Load/Unload) method, which can realize high recording capacity, has been employed. With the LUL method, at the halt stage, the magnetic head is evacuated to a tilting table called a ramp positioned outside of the magnetic disk. At the start-up stage, the magnetic head is loaded to a load zone on the magnetic disk surface from the ramp following the magnetic disk starting rotations, following which recording/reproduction is performed. Accordingly, the magnetic head is not subjected to contact sliding on the magnetic disk.
With this LUL method, the region for contact sliding of the magnetic head needs not to be provided on the magnetic disk surface unlike with the CSS method, the area of the region for recording/reproduction can be widely secured as compared with the CSS method, thereby providing an advantage wherein the recording capacity of the magnetic disk can be increased.
Also, with the LUL method, the magnetic disk is not in contact with the magnetic head, so that texture needs not to be provided, unlike with the CSS method, and the magnetic disk surface can be further subjected to smoothing. Accordingly, the LUL method also provides an advantage wherein the recording density of the magnetic disk can be improved by reducing flying amount of the magnetic head (e.g., 10 nm or less) lower than the case of the CSS method.
Incidentally, even with the magnetic disk to be mounted to a magnetic disk device employing the LUL method, a protective layer is provided to protect a magnetic layer formed on the disk substrate from corrosion and abrasion. The film thickness of this protective layer is preferably thick from the perspective of abrasion resistance, but spacing losses need to be reduced to achieve high recording density in recent years, and accordingly, reduction has been required for the film thickness of the protective layer as well.
The protective layer is formed on the magnetic layer normally using the sputtering method or the plasma CVD method, and the principal surface of the magnetic disk, i.e., the principal surface on which data is recorded, and the side surface portion are coated with the protective layer respectively. In this case, with the principal surface and the side surface portion of the magnetic disk, the protective layer is formed with generally the same film thickness. However, according to the studies of the present inventor, the present inventor found that with the side surface portion of the magnetic disk, the surface roughness is rougher than the principal surface highly subjected to accurate mirror surface formation in many cases, so even with the same film thickness of the protective layer as the principal surface, the adherability of the protective layer readily deteriorates. Accordingly, with the protective layer formed on the side surface portion of the magnetic disk, particles tend to occur due to contact, friction, and so forth with other members. The occurred particles may protrude as protrusions or cause contamination of the magnetic head, by adhering to the surface of the magnetic disk, for example.
Also, high smoothness of the magnetic disk surface is necessary in order for reducing flying height (flying amount) necessary for realizing high recording density of the magnetic disk. Due to further decrease of the flying amount of the recording head according to introduction of the recent LUL method, even with extremely low flying amount of 10 nm or less, for example, stable actions of the magnetic disk have been required. However, upon the magnetic head being subjected to flying flight on the magnetic disk surface with such an extremely low flying amount, there has been a problem in that fly-stiction frequently occurred. Fly-stiction is an obstacle wherein the flying attitude of the magnetic head suddenly becomes unstable during recording/reproduction, causing abnormal fluctuation in recorded signals and reproduced signals. This fly-stiction especially readily occurs with the magnetic head which performs flying with an NPAB (negative pressure air bearing surface) slider, i.e., a negative pressure slider. The magnetic head including a negative pressure slider has an advantage wherein stable flying flight can be performed even at a low flying amount of 10 nm or less, but this causes strong negative pressure upon the magnetic head undersurface (i.e., surface facing the magnetic disk). Accordingly, this readily causes fly-stiction.
Incidentally, with the LUL method, the flying amount of the magnetic head is greatly narrowed as compared with the conventional one, so that a serious problem readily occurs even with a surface defect (e.g., protruding defect) which has not been seen as a problem at all conventionally existing on the surface of the magnetic disk to be mounted on an HDD, for example. In particular, with a small-diameter magnetic disk to be mounted on a small HDD, the above problem becomes more serious. This is because occurrence of trouble is particularly concerning since such a small-diameter magnetic disk having an outer diameter of 30 mm or less, for example, is mounted in a mobile HDD such as a cellular phone, digital camera, and so forth, and is used under various harsh environments wherein impulsive force such as falling, collision, vibration, or the like exists consistently. Accordingly, improvement of the durable reliability of the magnetic disk has been further required.